The use of aluminum as a brake surface has not been known since no known friction material has been able to yield satisfactory performance in conjunction with an aluminum surface. Commercially available brake lining materials rubbing on an aluminum surface results in excessive aluminum wear rates and/or excessive brake lining wear rates.
The reason that aluminum wears rapidly or the lining used in conjunction therewith wears rapidly, is that the aluminum has a thin aluminum oxide layer thereon. This layer is hard and brittle and also has a low thermal expansion and thermal conductivity when compared to the base aluminum. High thermal fluxes are developed during braking operations. These thermal fluxes produce extremely high temperature "flashes" with locally high contact stresses between the brake lining material and the brake surface. These high temperature "flashes" have been found to fracture the aluminum oxide layer thereby providing hard, sharp cutting surfaces. These cutting surfaces cut into the brake lining material. The cutting of the lining in turn leads to irregular surfaces on the lining which tear out the small particles of aluminum oxide and some aluminum from the brake surface. These hard particles imbed themselves in the lining material and, in turn, cut into the aluminum brake surface. Consequently, both friction material and aluminum experience unacceptably high wear rates.
It is the object of this invention to provide a method for protecting a brake system which includes an aluminum brake and a brake lining.
It is another object of this invention to provide a method of protecting a brake system which includes an aluminum brake surface and a brake lining in which the cost of protection is relatively low and the protection provided remains over a substantial number of braking actions.
It is a further object of this invention to provide a method of protecting a brake system which includes an aluminum brake surface and a brake lining which is based on an asbestos formulation or a non-asbestos formulation.